Various techniques have been used to form objects with iridescent surfaces, i.e., a surface that appears to change color as the angle of view or the angle of illumination of the surface changes. In one example, a diffraction grating disposed on a surface is used to reflect or transmit different portions of incident light. The different light portions are seen as a view of an image that changes as the angle of incidence changes. In another example, multiple images are separated into strips, interlaced with each other on a surface, and overlaid with lenticular lenses. The lenses are aligned with the interlacing of the images so that light from each individual image is sent in a same respective direction. This configuration reveals different images to an observer over different view angles. In a further example, regions of a surface are embossed to have a periodic variation in a respective direction. The regions are colored with variations aligned with the periodic variation to enable a change in viewing angle to hide, subdue, or highlight one or more of the colors.
Known techniques of forming an iridescent surface on an object, such as the foregoing examples, generally consist of regions that only change color over a single view axis. For example, an image may change as an observer's view is shifted left-right, but does not change when the view is shifted up-down, or toward-away, or when the view is rotated. In another example, some iridescent paints, such as pearlescent paints, change color based on view angle, but change in the same manner regardless of view direction. Additionally, iridescent surfaces typically require a structured surface, e.g., a diffraction grating, lenticular lenses, or embossed ridges, or are limited in terms of what color changes are available. These structured surfaces increase the expense and complexity of forming an iridescent surface, and result in a surface that is susceptible to damage that can interfere with the intended coloration of the surface. Additionally, such structures are impractical or impossible to form on a three-dimensional printed object that has a non-planar or irregular shape that changes color along more than one axis.
Digital three-dimensional object manufacturing, also known as digital additive manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital model. Three-dimensional object printing is an additive process in which successive layers of material are formed on a substrate in different shapes. The layers can be formed by ejecting binder material, directed energy deposition, extruding material, ejecting material, fusing powder beds, laminating sheets, or exposing liquid photopolymer material to a curing radiation. The substrate on which the layers are formed is supported either on a platform that can be moved three dimensionally by operation of actuators operatively connected to the platform, or the material deposition devices are operatively connected to one or more actuators for controlled movement of the deposition devices to produce the layers that form the object. Three-dimensional object printing is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling.
Techniques have also been developed for coloring the surface of three-dimensional printed objects that include applying coloration after an object has been printed, and printing an object from different materials having different colors. However, three-dimensional printing has not been adapted to forming iridescent objects. Therefore, additive manufacturing processes that produce three-dimensional objects with surfaces having a coloration that changes when viewed at different angles and directions and illuminated with light from different angles would be beneficial.